The combined effect of steel fibres and high-range carbon nanotubes on properties of high-strength concrete

The present study investigated the effect of the addition of steel fibres (SFs) and the synergy of SFs and carbon nanotubes (CNTs) on the mechanical properties of high-strength concrete (HSC). The addition of CNTs prevents the growth of micro cracks during loading, creates a denser composite and enhances the bond between SFs and cement paste. Three samples of HSC with a compressive strength of 68 MPa as a control sample, HSC with 1% volume fraction of SFs (HSC + SF1), HSC with 1% volume fraction of SFs and 0.8% cement weight of CNTs (HSC + SF1 + CNT) were prepared. The mechanical properties of samples including compressive strength, tensile strength, modulus of rupture, stress-strain curves and water absorption were investigated. The CNTs were mixed using an ultrasonic device in superplasticiser and water for 50 min to disperse homogenously. The results showed that adding 1% SFs to concrete improved the properties of concrete. The combined usage of SFs and CNTs in concrete increased the compressive strength, tensile strength and modulus of rupture up to 13.1, 39.7 and 49.3%, respectively, compared to HSC, and 6, 12 and 14.6%, respectively, compared to HSC + SF1. Furthermore, the combined use of steel fibres and CNTs improved the toughness of HSC by 35% compared to HSC + SF1 and reduced water absorption of HSC by about 15%.